Field of the Invention
The present invention relates to pectate lyase variants exhibiting alterations relative to a parent enzyme; to a method of producing such enzymes; and to methods for using such enzymes in the textile, detergent and cellulose fiber processing industries. Compared to the parent enzyme, the pectate lyase variants of the present invention exhibit improved stability in detergents and/or improved thermal stability, e.g., in laundry processes and/or laundry and/or dishwash detergents.
Description of the Related Art
Pectin polymers are important constituents of plant cell walls. Pectin is a hetero-polysaccharide with a backbone composed of alternating homogalacturonan (smooth regions) and rhamnogalacturonan (hairy regions). The smooth regions are linear polymers of 1,4-linked alpha-D-galacturonic acid. The galacturonic acid residues can be methyl-esterified on the carboxyl group to a varying degree, usually in a non-random fashion with blocks of polygalacturonic acid being completely methyl-esterified.
Pectolytic enzymes (pectinases) can be classified according to their preferential substrate, highly methyl-esterified pectin or low methyl-esterified pectin and polygalacturonic acid (pectate), and their reaction mechanism, beta-elimination or hydrolysis. Pectinases can be mainly endo-acting, cutting the polymer at random sites within the chain to give a mixture of oligomers, or they may be exo-acting, attacking from one end of the polymer and producing monomers or dimers. Several pectinase activities acting on the smooth regions of pectin are included in the classification of enzymes provided by the Enzyme Nomenclature (1992) such as pectate lyase (EC 4.2.2.2), pectin lyase (EC 4.2.2.10), polygalacturonase (EC 3.2.1.15), exo-polygalacturonase (EC 3.2.1.67), exo-polygalacturonate lyase (EC 4.2.2.9) and exo-poly-alpha-galacturonosidase (EC 3.2.1.82).
Pectate lyases have been cloned from different bacterial genera such as Erwinia, Pseudomonas, Klebsiella and Xanthomonas. Also from Bacillus subtilis (Nasser et al. (1993) FEBS 335:319-326) and Bacillus sp. YA-14 (Kim et al. (1994) Biosci. Biotech. Biochem. 58:947-949) cloning of a pectate lyase has been described.
Variants of a pectate lyase from Bacillus subtilis have been disclosed in patent applications WO 2002/092741 and WO 2003/095638.
The pectate lyases are generally characterised by an alkaline pH optimum and an absolute requirement for divalent cations, Ca2+ being the most stimulatory.
It is an object of the present invention to provide a cell-wall degrading enzyme variant, a pectin-degrading enzyme variant, especially a pectate lyase enzyme variant, which exhibits improved performance over the parent pectate lyase when applied e.g. in detergents or in textile industry processes.